The present invention relates generally to a parameter monitoring system and more particularly to a remote monitoring system and indicator by means of which an inaccessible fault can be quickly sensed and identified.
It is often essential for parameters such as pressure, temperature or the like to be continuously monitored at inaccessible locations, and a warning be quickly provided when the monitored parameter has varied beyond a preselected range. The problem is particularly complex in situations where electric power cannot be conveniently provided to the remote location.
A typical application, and one in which the present invention will be illustrated, is a helicopter in which the structural integrity of the blades must be continuously monitored; it having been found that a crack in a blade spar if not detected will quickly result in deterioration of structural integrity (fatigue) and eventually the inability of the aircraft to maintain altitude. It is desirable, if not essential, to be able to detect crack development long before blade failure, to permit replacement or repair.
For these reasons helicopters are frequently provided with a variety of preflight and postflight blade structural integrity monitoring systems for inspection by the helicopter pilot during static conditions (blades at rest). In such systems the blade spar is hollow and a predetermined pressure (above or below ambient) is sealed in the blade cavity. In known monitoring systems, a differential sensing the visual indicator, such as that disclosed in U.S. Pat. No. 3,417,727 (to this assignee) is incorporated in the blade systems. Upon occurrence of a fissure in the spar, the pressure is altered and the change sensed to provide a visual indication. While devices of this type are highly reliable in sensing and indicating the existence of a developing crack, such apparatus is limited to static environments (when the blade is at rest). However, longer flight requirements for helicopters and greater helicopter loads have necessitated systems which can monitor blades in flight and under load so that a real time observation may be afforded the pilot. Such systems are fraught with problems. The most significant of which is the sensing of the fault within the cockpit confines. The use of slip rings to transmit such faults to the cockpit is both expensive and unreliable.
One such arrangement is described in U.S. Pat. No. 3,739,376 (to this assignee) wherein the differential pressure sensor activates a passive element (tuned circuit) housed in the blades of the helicopter which element is electromagnetically coupled to an active unit in a more accessible location. While such an arrangement accomplishes its objectives, it requires modification to the helicopter blade and rotor which is sometimes undesirable.
It is, therefore, an object of this invention to provide a remote monitoring system in which parameters such as pressure can be accurately sensed at relatively inaccessible locations with little to no modification of the apparatus in which it is being used.
It is another object of this invention to provide a monitoring system in which no energy need be supplied to the parameter sensing unit, as for example where the parameter to be sensed is in a remote and inaccessible environment, in particular a helicopter rotor blade.
It is a further object of this invention to provide a remote parameter monitoring system for helicopters which is capable of operating through a single blade port with an indicator not too different than that disclosed in U.S. Pat. No. 3,417,727, a conventional, reliable and widely used indicator.
It is a further and specific object of this invention to provide a remote pressure sensing and monitoring system for use in a vehicle in which the occurrence of a potentially dangerous pressure change, such as in a helicopter rotor blade, can be quickly observed by the operator of the vehicle while the vehicle or its monitored parts are operating under load or are in motion.
It is still a further object of this invention to provide such a remote pressure sensing and monitoring system as will satisfy the foregoing objects with snap or trigger action. That is, may employ a mechanical amplifier to utilize a small mechanical trigger to activate a larger force.